The FM mobile radio marketplace demands a wide variety of different optional features to meet diverse customer requirements. Thus, it is desirable to provide a radio having signalling options such as continuous tone controlled squelch (CTCSS), selective call decoding (a paging function using a set of signalling tones), DTMF encoding for generating tones to enable interconnection with a telephone system, automatic transmission (upon keying the transmitter) of status and identification data messages (e.g., for police use), etc. These and/or similar functions also can be implemented using digital signals rather than tones.
While it is highly desirable for a portable FM mobile radio to have the capability of supporting these various options, cost and size constraints generally preclude the incorporation of all functions in a single package. The design of the present invention serves to produce a radio capable of a multitude of various system configurations, none of which burden the simplest version of the product.
Early designs of portable FM mobile radios attempted to achieve this same result by adding hardware modules to the basic radio. The resulting increase in the size of the radio and the associated mechanical design complications are obvious disadvantages of such a solution. In addition, due to constraints of the hardware design, the types of functions which may be added to the radio are significantly limited.
With the development of low current, low cost, single chip microprocessors, software implementation of many of the control and signaling functions in portable radios has become practical. However, due to limitations in the ROM size of such microprocessors, there is a limitation as to the number of functions which may be incorporated therein due to the storage space required to implement the basic radio control functions.
Additionally, low processing speeds associated with such prior art microprocessor control typically prevented software versions of certain signaling functions from being practically implemented. For example, the selective call decoding option referred to above may involve decoding tones that are of a sufficiently high frequency that it is difficult for a microprocessor to execute a tone decoding routine fast enough to have time to perform the basic radio control software functions as well.
In the portable radio art, only single chip microprocessors are commercially practical for FM portable mobile radio applications (due chiefly to size and power consumption considerations). In this art, the addition of future options typically required remasking the basic control processor, adding lost time and risk to the manufacturing process.
The present invention provides a basic portable FM mobile radio design capable of future functional expansion by utilizing a unique microprocessor hardware/software control system. The radio includes a control microprocessor which is capable of performing all the basic radio control functions. In addition, options are added via a plug-on board that includes an options microprocessor which interfaces with the control microprocessor over a data bus and with the radio's audio circuits through audio processing circuitry. The software of the system allows control to be passed to the option board.
The radio operates in a standard control mode and an option control mode. In the standard mode, in which no option board is present, the control processor performs all basic radio control functions. In the option mode, where the option control microprocessor is present, the main control processor typically receives commands from the option board. The multiprocessor design of the present invention enhances overall processing speed by utilizing parallel processing where one processor performs basic control functions while the other performs optional dedicated tasks.